A NEW TYPE OF FLEXOR TENDON REPAIR Biomechanical evaluation by cyclic loading, ultimate strength and assessment of pulley friction in vitro R. J. N. WILLIAMS and A. A. AM-IS From the Biomechanics Section, Department of Mechanical Engineering, Imperial College of Science, Technology and Medicine, London, UK Experiments were performed to evaluate biomechanical aspects of the performance of a "deep- biting peripheral suture" for flexor tendon repair, either when used alone or with a square or modified Kessler core stitch, and the technique was compared to the Kleinert repair. Tests included progressively increasing cyclic loads, force to pull the repair into the A2 pulley, and ultimate failure strength. 50% of the Kleinert repairs failed under 30 N cyclic loading, while 100% of the DBPS plus Kessler core stitch repairs survived. There was no discernable difference in gliding function or repair bulk between these sutures, but ultimate strength increased significantly with the DBPS repairs. We concluded that the DBPS plus Kessler-type core stitch will survive active mobilization better than the Kleinert method. Journal of Hand Surgery (British and European Flexor tendon repair, particularly in zone 2 or "no- man's land", is still a surgical challenge and much work on repair techniques, materials, the biology of tendon healing and rehabilitation has not settled the issue. It is now recognized that tendons can heal directly without granulation tissue in-growth from the synovial sheath (Manske et al, 1984) and regimens for passive and later active mobilization following repair were based on this finding. The forces that are thought to act through an FDP tendon during passive and active unopposed flexion are 0.1 N (range 0.1-0.2) and 19.0N (1.0-29), respectively (Schuind et al, 1992). Therefore any new or modified repair technique has to withstand these forces if rapid rehabilitation is to be achieved. Previous work from this institution has shown that a peripheral deep biting continuous suture technique (DBPS; Fig 1) was strong enough to allow active flexion after repair (Mashadi and Amis, 1992). That work, however, did not combine the peripheral suture with a core suture of any type. One aim of this study was to see if a combined technique with peripheral and core sutures would confer any additional benefit as regards gap formation and failure strength. A separate study by Mashadi and Amis (1991) using X-ray analysis of stainless steel "modified Kessler" sutures (Kleinert et al, 1981) showed that the locking loops used in this type of repair tended to pull out under load. We decided to investigate whether this technique predisposed to gap formation as was suggested, when used in combination with the new deep-biting peripheral suture (DBPS), and C__ _ , Fig 1 Diagram of the deep biting peripheral suture (DBPS) with the knot tied within the repair. Volume, 1995) 20B." 5:578-583 to employ the commonly-used technique of Kleinert et al (1981) for comparison with the new technique. Rather than simple load-to-failure testing, cyclic load- ing of flexor tendon repairs has been shown to be a more sensitive method of inducing gap formation and more closely simulates early mobilization (Pruitt et al, 1991). We devised a protocol for cyclic loading of our repairs using a materials testing machine. We expected the new combined DBPS plus Kessler core stitch repair to be stronger than the standard Kleinert repair, but were also interested in whether it would move or glide through the fibrous pulley system as well. To study this, we used an apparatus described by Coert et al (1994), wherein tendon repairs are pulled proximally into the A2 pulley on a dissected digit and the increased forces generated by the repair entering the pulley are recorded. We hoped by these means to obtain laboratory data on the relative performance of the suturing methods that related as closely as possible to clinical conditions. MATERIALS AND METHODS FDS and FDP tendons from index, middle and ring fingers, together with the FPL tendon, were harvested from cadavers within 24 hours post mortem. They were kept moist with Hartman's solution, sealed in containers and frozen to -18°C. Cyclic loading of tendon repairs Four types of repair were compared, with ten repairs in each group. The deep biting peripheral suture (DBPS) first described in detail by Mashadi and Arnis (1992) was used in three of the four groups: 1) DBPS alone; 2) DBPS combined with a modified Kessler core suture, and 3) DBPS combined with a simple square suture to bring the tendon ends together. The fourth type was the commonly-used modification of the Kessler/Kirchmayr 578